Generally, the object of IEEE802.21 in progress for International Standardization of inter-heterogeneous-network media independent handover is to enhance user's convenience for mobile terminal devices by providing seamless handover and service continuity between heterogeneous networks. MIH function, event trigger, command service and information service (IS) are defined as basic requirements.
A mobile subscriber station is a multi-mode node that supports at least two interface types. And, an interface can be implemented in various types. For instance, a wire-line type interface such as 802.3-based Ethernet, a wireless interface type based on IEEE802.XX such as IEEE802.11, IEEE802.15, IEEE802.16 and the like, an interface type defined by cellular standardization organization such as 3GPP and 3GPP2 and the like are possible.
FIG. 1 is a diagram of protocol architecture of a multi-mode mobile subscriber station. Referring to FIG. 1, a multi-mode mobile subscriber station has a physical layer per mode and a medium access control layer per mode. And, an MIH layer lies below an IP layer.
Media independent handover (MIH) should be defined between IEEE802-series interfaces or between the 802-series interfaces such as the above-mentioned non-802-series interfaces defined by the cellular standardization organization such as 3GPP and 3GPP2. And, a mobility supporting protocol of an upper layer such as Mobile IP and SIP (session initiation protocol) should be supported for the seamless handover service.
MIH function is placed below an IP layer and facilitates a handover handling process using a trigger event and an input value from a second layer (Layer 2) such as information of other networks and the like. The MIH function can include input values based on user policy and configuration that can put influence on a handover process, and general interfaces are defined between the MIH function and a third layer (Layer 3) entity such as Mobile IP and SIP. These interfaces provide information about a first layer (Layer 1) (physical layer), the second layer (Layer 2) (MAC layer) and mobility management, and the MIH acquires information about lower layers and network with the help of the event and information service.
Hence, the MIH function should be placed in a higher layer to monitor and control statuses of other links within the mobile subscriber station. FIG. 2 is a diagram of functional entities and transport protocol of a terminal including an MIH function and a network, in which dotted lines indicate a primitive, an event trigger and the like.
For fast handover, a network layer needs to use information from a link layer to re-establish a connection as soon as possible. A link layer event helps to estimate a user's movement and may help a mobile subscriber station and network to prepare handover in advance.
A trigger for handover may start from a physical layer (PHY) and a medium access control layer (MAC). An origin of this trigger may be a local stack or a remote stack. FIG. 3 is a diagram of a trigger model.
An event trigger provides a state of a current signal, a state change of another network and an estimated change and also provides a change between a physical layer and a medium access control layer and attribute changes of a specific network.
Event types can be classified into PHY layer event, MAC layer event, Management event, L3 event, Application event and the like.
A basic trigger event is explained as follows.
First of all, ‘Link_Up’ occurs in case that a Layer 2 connection is established on a specific link interface and in case that L3 packets can be transferred from a higher layer. In this case, it is decided that all L2 configurations configuring the link are completed. And, event origins are ‘Local MAC’ and ‘Remote MAC’. Parameters of ‘Link_Up’ are shown in Table 1.
TABLE 1NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from whichevent isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich event shallbe deliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofold access routerMacNewAccessRouterMAC AddressMAC address ofnew access routerNetworkIdentifierMedia SpecificNetworkIdentifier usablein detectingchange of subnet
‘Link Down’ occurs in case that an L2 connection is released on a specific interface and in case that it is unable to transfer L3 packets anymore. And, an event origin is ‘Local MAC’. Parameters of ‘Link Down’ are shown in Table 2.
TABLE 2NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from whichevent isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich event shallbe deliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofold access routerReasonCodeReason why linkis released
‘Link_Going_Down’ occurs in case that it is estimated that an L2 connection is going to link down within a specific time. And, ‘Link Going Down’ may be a signal for initializing a handover procedure. Event origins are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Going_Down’ are shown in Table 3.
TABLE 3NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin fromwhich event isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich eventshall bedeliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofold accessrouterMacNewAccessRouterMAC AddressMAC address ofnew accessrouterTimeIntervalTime in msecsEstimated timefor Link_DownConfidenceLevel%Estimatedlevel forLink_Down oflink in aspecific timeUniqueEventIdentifierUsed in casethat Eventrollbackoccurs
‘Link_Going_Up’ occurs in case that it is estimated that an L2 connection is going to ‘link up’ within a specific time. And, ‘Link Going Up’ is used in case that it takes a long time for a network to be initialized. Event origins are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Going_Up’ are shown in Table 4.
TABLE 4NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin fromwhich event isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich eventshall bedeliveredMacMobileTerminalMAC AddressMAC address ofMSSMacOldAccessRouterMAC AddressMAC address ofold accessrouterMacNewAccessRouterMAC AddressMAC address ofnew accessrouterTimeIntervalTime in msecsEstimated timefor Link_UpConfidenceLevel%Estimatedlevel forLink_Up oflink in aspecific timeUniqueEventIdentifierUsed in casethat Eventrollbackoccurs
‘Link_Event_Rollback’ is combined with ‘Ling_Going_Up’ or ‘Link_Going_Down’ to use. It is a trigger occurring in case that ‘Ling_Going_Up’ or ‘Link_Going_Down’ is estimated not to occur within a specific time anymore despite that ‘Ling_Going_Up’ or ‘Link_Going_Down’ is transmitted. Event origins are ‘Local MAC’ and ‘Remote MAC’. Table 5 shows parameters of ‘Link_Event_Rollback’.
TABLE 5NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin fromwhich event isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich eventshall bedeliveredMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC address ofnew accessrouterUniqueEventIdentifierUsed in casethat Eventrollbackoccurs
‘Link_Available’ indicates that a new specific link is usable or available. ‘Link_Available’ indicates possibility that a new base station or access point can provide a link quality better than that of a base station or access point currently accessed by a mobile subscriber station. Event origins are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Available’ are shown in Table 6.
TABLE 6NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin from whichevent isgeneratedEventDestinationEVENT_LAYER_TYPEDestination towhich event shallbe deliveredMacMobileTerminalMAC AddressMAC address ofMSSMacNewAccessRouterMAC AddressMAC address ofnew access routerMacOldAccessRouterMAC AddressMAC address ofold access router
‘Link_Parameters_Change’ is an event occurring in case that a variation of a link parameter value exceeds a specific limit. This can include a link layer parameter such as a link speed, QoS (quality of service), encryption value and the like. Event origins are ‘Local MAC’ and ‘Remote MAC’. And, parameters of ‘Link_Parameters_Change’ are shown in Table 7.
TABLE 7NameTypeDescriptionEventSourceEVENT_LAYER_TYPEOrigin fromwhich eventis generatedEventDestinationEVENT_LAYER_TYPEDestinationto whichevent shallbe deliveredMacMobileTerminalMAC AddressMAC addressof MSSMacAccessRouterMAC AddressMAC addressof currentaccessrouteroldValueOfLinkParameterOld value oflinkparameternewValueOfLinkParameterNew value oflinkparameter
FIG. 4 is an exemplary diagram of a trigger occurring until a new link is created since a quality of link currently accessed by a mobile subscriber station is degraded.
Information Service provides detailed information for a network necessary for network discovery and selection and should be accessible by any kind of network. The information service should include information elements such as link access parameter, security mechanism, neighbor map, location, service provider and other access information, cost of link and the like.
‘Mobile IPv4’ is explained as follows.
First of all, a configuration of network supporting Mobile IP includes a home agent, a foreign agent and a mobile terminal. For operation of Mobile IP, functions of agent discovery, registration, routing, temporary address (CoA) and the like are required. Each of theses functions are explained as follows.
First of all, agent discovery is a method that a mobile terminal decides whether it is connected to a home network or located at a foreign network. By this method, the mobile terminal is able to detect that it has been moved away into another network.
The registration function provides flexible mechanism enabling a mobile terminal to be provided with a service, which has been provided to the mobile terminal on a home network, on a new network by delivering current location information to a home agent in case that the mobile terminal detects that it has been moved away into another network.
The routing function is needed to appropriately perform routing on datagram to be transmitted/received by a mobile terminal in case that the mobile terminal is connected to a foreign network.
The temporary address (CoA) function is to establish a temporary address in case that a mobile terminal is moved away into another subnet. The temporary address function can provide temporary address possibility by two kinds of methods ‘FA-CoA’ and ‘co-located CoA’. The ‘FA-CoA’ method is provided by a foreign agent via an agent advertisement message, and an IP address of the foreign agent is used as a temporary address. The ‘co-located CoA’ method is a method that a temporary address is allocated to a moving node via a DHCP server located at a foreign network.
The basic object of Mobile IPv4 is to support transparent mobility of an upper layer and needs additional functions of mobile host, home agent and foreign agent. Yet, in case of not using path optimization, a change of a correspondent node communicating with a mobile terminal is unnecessary. In this case, the mobile host represents an IP host supported by mobility. The home agent is a router that sustains location information for the mobile host and performs tunneling. And, the foreign agent means a router supporting mobility in a foreign network.
FIG. 5 is a diagram for explaining basic operations in Mobile IPv4. Operations in the respective steps of FIG. 5 are explained as follows.
(1) In case that a mobile host moves away into a foreign network from its home network, the mobile host recognizes that it has moved by receiving an advertisement message broadcast from the foreign network and then registers a temporary address (CoA) indicating its current location to a home agent in the home network.
(2) In this case, CoA is an IP address (FA-CoA) of a foreign agent or an address allocated to the mobile host via DHCP or the like by the foreign network. Packets sent to the mobile host from outside are transferred to the home network and these packets are picked up by a home agent recognizing a movement of a mobile terminal.
(3) The home agent encapsulates a packet delivered to the mobile host by targeting an address of FA as a destination and then delivers it to the foreign agent.
(4) The delivered encapsulated packet is recovered into an initial delivery packet by being de-capsulated by the foreign agent and is then delivered to the mobile host finally.
(5) The packet to be delivered to a correspondent host from the mobile host can be directly delivered via the foreign agent or can be delivered using a reverse tunnel in case of a problem of ingress filtering.
A medium access control (MAC) layer of a multi-mode mobile terminal transmits ‘Link_Going_Down’ trigger to MIH if a signal quality of a currently connected link is degraded. The medium access control layer then executes a scanning process. In doing so, if a new link is searched from a medium access control layer of another interface, a process for releasing a connection with a previously connected link is necessary after creation of link. Yet, it is unable to perform this process with a conventional trigger only.